1. Field of the Invention
The present invention relates to an electronic circuit device in which a driver IC, a memory, a controller and the like for driving a liquid crystal used in portable equipment, etc. and electronic pocketbooks are mounted in bare chips, or unpackaged.
2. Description of the Related Art
To join a semiconductor device to a circuit board by adhesion, the following conventional bare chip mounting techniques are available for semiconductor ICs. One technique involves the step of compression-bonding with an anisotropic conductive film to the circuit board using plated projecting electrodes of bumps, which are Au bumps formed on the IC pad by plating, or using stud bumps which are developed by wire bonding technology. Another technique involves the steps of transferring a silver paste onto the bumps for joining to the board and causing an underfill to fill up the space therebetween.
To join a semiconductor device to a circuit board by metal diffusion, the following conventional techniques are available. One technique involves the steps of preparing bumps made of a solder on an IC, soldering the bumps to the electrode of a board, and causing an underfill to fill up the space therebetween. Another technique involves the steps of preparing Au bumps on an IC, plating the electrode of a board with Sn, joining the IC to the board by the diffusion of Au and Sn, and causing an underfill to fill up the space therebetween.
FIG. 4 is a sectional view of a related art showing an electric circuit device. The device has a pattern 2 for electrically connecting an integrated circuit 4 to a peripheral circuit on an insulating substrate 1. The space between the lower surface of the integrated circuit 4 and the insulation substrate 1 is filled with an anisotropic conductive film 5.
In any joining technique, the joint reliability of a semiconductor IC requires that the underfill or a binder of the anisotropic conductive film have certain properties. In order for the underfill or the binder of the anisotropic conductive film to have a long-term reliability that may be impaired due to differences in the coefficient of linear expansion between the IC and the circuit board, such properties as the holding force at the time of curing, coefficient of linear expansion, and Young""s modulus are important.
However, there is a mechanism which breaks the joint between the IC and the circuit board. That is, the joint is severed as the underfill or the binder of the anisotropic conductive film is peeled off from an area of the insulating substrate which is closer to the center than the bumps of the mounted IC. Particularly, in the case of COF in which a semiconductor IC is mounted on a film substrate that is formed by evaporating and plating Cu on a polyimide film, the adhesion of the IC to the polyimide film is so poor that no improvement in reliability has been made.
An object of the present invention is to overcome this problem.
To overcome this problem, in an electronic circuit device wherein an IC is mounted facedown at least on a circuit board, the IC is connected to the circuit board by reinforcing the adhesion of a circuit surface of the IC to the circuit board while causing an underfill made of an adhesive or causing a binder in the case of an anisotropic conductive film to fill up an area excluding an electrode connecting portion.
Here the circuit board has a pattern formed for connecting the board to the IC, and also has another pattern that is formed to connect to a dummy or part of electrical signal terminals adjacent to that pattern. Thus, the area where the IC adheres to the insulating substrate made of polyimide or the like is reduced and the area where the IC adheres to the pattern having a greater adhesive strength than polyimide is increased, and thus the reliability is improved.
The electronic circuit device that is constructed as described above provides an improved reliability against thermal stresses between the board and the IC caused by temperature fluctuations or the like. As a result, an electronic circuit device having a stable quality can be obtained.